The air outlets of the air conditioning unit, hereinafter referred to as outlets, are the interfaces at which air flow ducts are connected during assembly of the motor vehicle. The air flow ducts, referred to hereinafter as ducts for short, direct the air conditioned in the air conditioning unit to the air discharge vents at defined locations in the motor vehicle, wherein the term air discharge vent is understood to mean the visible openings in the motor vehicle ventilation system, from which the air is directed and from which it flows at a desirable velocity directly into the interior of the motor vehicle.
Outlets of the aforementioned kind are connected directly or by way of ducts with defined air discharge vents. In the selected embodiments the defrost outlet is connected directly to the defrost air discharge vents for supplying air to the front windshield, whereas the side window air outlets are connected with the side window air discharge vents and the side occupant air outlets and center occupant air outlets are connected by way of ducts to the side occupant and center occupant air discharge vents in the instrument panel. For the latter, the terms dashboard vent, air vent, air discharge panel, side or center air nozzle are also frequently use.
An arrangement of air flow ducts is described in U.S. Pat. Appl. Pub. No. 2010/0178861 A1, in which the ducts exiting from the left and the right defrost outlet of the vehicle air conditioning unit are crossed and hence are directed to the right and the left side of the front windshield. This configuration is intended to enable fresh air to exit the air discharge vent at a very shallow angle in the direction of the windshield, thereby also reaching, in sufficient amount, both extreme corners of the windshield, and thus eliminating any frost that may be present. However, this arrangement entails accepting the drawback that the crossover of the air flow ducts requires additional installation space and that the additional components also mean adding weight to the air conditioning system.
A duct arrangement inside the instrument panel is described in PCT Pat. Appl. Pub. No. WO 03/033310 A1, specifically the position of the center occupant air flow ducts in the direction of the front-seat passenger, wherein the problem lies mainly in the positioning of the airbag module and areas of potential head impact in the event of an accident.
Air flow ducts which direct the air to the sides of the motor vehicle are normally longer and hence, exhibit higher loss of pressure than air flow ducts that distribute the air from air discharge vents centrally located in the vehicle interior. To ensure equal distribution of the air volume in the transverse direction of the vehicle, the pressure loss of the former mentioned ducts is increased artificially in prior art implementations by selectively throttling the air flow with the aid of corresponding dampers in the air conditioning unit. However, this results in higher flow velocities in the vicinity of the dampers, which results in a reduction of the overall air volume and a significantly higher level of noise in the vehicle interior must be tolerated. This technical solution also leads to the disadvantages of additional components, additional required installation space, and with that, added weight to the air conditioning system.
Design specifications, such as the placement of a clock, a loud speaker, or a display in the center of the instrument panel frequently also restricts the installation space for the air flow ducts and the center occupant air discharge vents, requiring at the same time greater functionality of the air conditioning unit such as, for example, additional air venting from the instrument panel that is not perceived by the vehicle occupants as a direct air stream, but nevertheless contributes to improved air conditioning of the vehicle interior and is located in the same position as the center occupant air discharge vent in the air conditioning unit. For this purpose, it is necessary to divert the air flow ducts from the center of the air conditioning unit around these additional components by means of appropriate diversions and diameter changes, which also leads to a relatively significant drop in pressure and to greater noise in the passenger compartment.
Moreover, modern vehicle designs frequently necessitate a flatter windshield and reduced height of the installation space for the air conditioning unit, including the air flow ducts and the instrument panel. For this reason, the air flowing from the defrost outlet toward the windshield must be fanned out at increasingly shorter distances over the entire width of the windshield.
In a conventional two-tier arrangement of outlets on a motor vehicle air conditioning unit according to the prior art, as shown in FIG. 1, this problem is exacerbated by the air being tapped from the side-window outlets directly adjacent to the defrost outlet. This further restricts the potential width of the defrost outlet, and thus, given the restricted height of the installation space, impedes the distribution of air over the entire width of the windshield. This effect is inconsistent with the requirement of a balanced air flow distribution at the air discharge vents in the vehicle interior.